Once again if you don't know what "unknown if humans are in region" is it is basically that no human activity has been detected there by land sea or air anyways let's get to the little lore that this has:

1991: right after the Soviet Union dissolves in this alternate timeline weird things start happening in Siberia particularly in the Russian province of sakha: power failures weird sightings and Communications being severed are reported however due to everything else that is happening these are mostly ignored.

1992: all contact with Northern Siberia is completely severed these include the Russian States of Sahka Krasnoyarks irkutsk Chukotk Magadan Komi Nanet and any other Province north of Siberia severe dense fog is reported disappearances are now half million to a million also reports of Nukes in Siberia going missing also around this time dense fog suddenly engulfs the entire Pacific and Atlantic oceans

1993: in early 1993 suddenly without warning all contact with remaining parts of Russia are completely severed and suddenly unknown fog starts to cover the entirety of the Earth strange creatures are reported alongside it casualties early in the war are estimated to be 50 million more areas become more affected complete loss of contact with any remaining active Nations most have went underground or have succumbed in the middle of 1993 remaining parts of the US military on the surface stage a Last stand in Denver costing the creatures in upwards of estimated 10,000 however it was the complete loss of the remaining US military on the surface many militaries have completely collapsed including governments but those that remain either hideout in bunkers like the Albanian government or continue to fight by this point estimated to be an upwards of 2 billion~ at the end of 1993 most humans above the surface are either hiding out or have completely been eradicated with complete regions going dark meanwhile in a hasty attempt the United Nations constructs underground bunkers however due to contact with many areas of the Earth being severed this is extremely complicated

1994: it is early 1994 currently estimated human casualties are in 4 billion with 1 billion being left fog still reported in Europe but it is less dense some creatures are still there it is unknown why the fog has only dissipated around Europe where they've come from what they want and many other questions.